In the complaint filed on May 4, the publisher claims Tumblr failed to remove more than 200 copyrighted photos posted by its users even after Perfect 10 sent six Digital Millenium Copyright Act takedown requests. What's more, Photo District News reports that many of the images contained watermarks or other copyright notices.

Tumblr's reliance on pornographic content and copyrighted material has made news before. In September 2011, CBS News reported on the blog hosting site's "dark side," drawing attention to porn-related searches of the site and calling it "the perfect vehicle for image porn."

It also observed that, if the site's users were to monetize blogs that used copyrighted material, "lawyers will descend on Tumblr and its users like lions on an injured antelope."

Tumblr's terms of service prohibits the use of copyrighted material on users' blogs, stating that the company may "immediately terminate or suspend" accounts that are repeatedly flagged for copyright infringement.